The objective of the investigation proposed here is to complete the development of a prototype ammonium ion specific electrode which can operate at physiological pH's and to demonstrate its utility for the simple and rapid diagnostic profiling of several important clinical chemistry constituents in human sera: urea, trypsin, glutamic oxaloacetate transaminase (GOT) inorganic ammonia, and orithinine carbonyl transferase (OCT). The prototype ammonium ion specific electrode was developed under a previous NIH grant. The proposed research work consists of experimental verification of a theory developed by GSRI investigators for increasing the speed of response of the ammonium ion specific electrode at physiological pH's and adaptation of the refined electrode to screening in real life situations - i.e., in the biological matrix, human serum. The ammonium ion specific electrode consists of a glass monovalent cationic electrode covered with a polymer membrane permeable to NH3 which is generated from the equilibrium reaction, NH4 yields (reversibly) NH3 plus H ion, but not permeable to K ion and Na ions. The speed of response of the electrode will be increased via studies with both solubility barriers and vapor barrier thin membrane and hollow fibers of high ammonia permeability.